1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a double reduced data (DRD) pixel structure wherein reduction of an aperture ratio is minimized, thereby improving image quality.
2. Discussion of the Related Art
In recent years, displays to visually express an electric information signal have been rapidly developed. As a result, various kinds of small and lightweight flat display devices having low power consumption have been developed and rapidly replaced conventional cathode ray tubes (CRTs).
Examples of the flat display devices include a liquid crystal display (LCD), an organic light emitting display (OLED), an electrophoretic display or electric paper display (EPD), a plasma display panel (PDP), a field emission display (FED), an electroluminescent display (ELD), and an electrowetting display (EWD). These displays commonly require a flat display panel on which an image is displayed. The flat display panel includes a pair of substrates coupled to each other while an inherent luminous material or polarizing material layer is disposed therebetween. The LCD is a typical example of a flat display device. The LCD adjusts light transmissivity of a liquid crystal using an electric field to display an image.
A general liquid crystal display device includes a lower substrate and an upper substrate disposed opposite to each other, a liquid crystal layer filling a space defined between the lower substrate and the upper substrate, a transistor array at the top of the lower substrate to define a plurality of pixel regions corresponding to a plurality of pixels and to control light transmissivity of the liquid crystal layer corresponding to the respective pixel regions, pixel electrodes and common electrodes alternately formed on the pixel regions, black matrices formed at the rear of the upper substrate to prevent light leakage around the pixel regions, and gate driver integrated circuits (hereinafter, referred to as “gate D-ICs”) to apply a gate signal to the transistor array and data driver integrated circuits (hereinafter, referred to as “data D-ICs”) to apply a data signal to the transistor array. The transistor array includes gate lines and data lines intersecting to define the respective pixel regions and a plurality of transistors disposed at regions where the gate lines and the data lines intersect. The transistors are connected to the pixel electrodes respectively.
In the liquid crystal display device with the above-stated construction, the transistors corresponding to the respective pixels are selectively turned on in response to the gate signal, and pixel voltage corresponding to the data signal is applied to the pixel electrode connected to the turned-on transistor to generate a predetermined electric field between the pixel electrode and the common electrode. The direction of liquid crystal cells is changed according to the generated electric field, thereby adjusting light transmissivity of the respective pixels, i.e., brightness, and thus the liquid crystal display device displays an image.
Meanwhile, the gate D-ICs generate a gate signal to sequentially turn on the transistors. The gate D-ICs may be embodied using relatively simple circuits. On the other hand, the data D-ICs connected to the data lines must generate a data signal corresponding to the respective pixels. For this reason, the data D-ICs are embodied using more complicated circuits than the gate D-ICs. There has been proposed a liquid crystal display device having a double reduced data (DRD) pixel structure in which two neighboring pixels share a data line disposed therebetween, and therefore, the number of the data D-ICs, which are more expensive than the gate D-ICs, is cut in half, thereby reducing manufacturing costs.
FIG. 1 is an equivalent circuit diagram of a general liquid crystal display device having a DRD pixel structure. FIG. 2A is a plan view illustrating a conventional liquid crystal display device having a DRD pixel structure, and FIG. 2B is an image illustrating a light discharge surface of the liquid crystal display device shown in FIG. 2A.
As shown in FIG. 1, pixels P1 and P2 disposed in two neighboring columns are commonly connected to a data line DL disposed between the two neighboring columns. The first pixels P1 commonly connected to the data line DL are connected to a first gate line GL1, and the second pixels P2 commonly connected to the data line DL are connected to a second gate line GL2.
Specifically, as shown in FIG. 2A, a conventional liquid crystal display device having a DRD pixel structure includes first gate lines GL1 and second gate lines GL2 alternately disposed in the horizontal direction, data lines DL and common lines CL alternately disposed in the vertical direction, transistors TFT1 of first pixels P1 disposed at regions where the first gate lines GL1 and the data lines DL intersect, transistors TFT2 of second pixels P2 disposed at regions where the second gate lines GL2 and the data lines DL intersect, pixel electrodes PX and common electrodes CX alternately formed at respective pixel regions defined by the first gate lines GL1 or the second gate lines GL2 and the data lines DL, shield lines SL extending from the common lines CL such that the shield lines SL are disposed at opposite sides of the data lines DL in parallel, and storage capacitors Cst formed by at least partial overlap between horizontal regions of the pixel electrodes PX and lower electrodes extending from the common lines CL at the pixel regions. In the first pixels P1 or the second pixels P2, the pixel electrodes PX are connected to the first transistors TFT1 or the second transistors TFT2 via pixel electrode contact holes CTpx, and the common electrodes CX are connected to the common lines CL via common electrode contact holes CTcx. The storage capacitors Cst are connected in parallel between the common electrodes CX and the pixel electrodes PX such that voltage difference between the common electrodes CX and the pixel electrodes PX is maintained for a predetermined time even after the transistors TFT are turned off. The shield lines SL prevent liquid crystal cells from malfunctioning due to electric potential of the data lines DL to which a data signal is applied.
In the related art, however, the storage capacitors Cst partially occupy the pixel regions, with the result that an aperture ratio is reduced in proportion to the size of the pixel regions occupied by the storage capacitors Cst.
Since the data lines DL and the shield lines SL are adjacent to each other, a predetermined electric field may be generated between the data lines DL to which the data signal is applied and the shield lines SL to which common voltage is applied. Directions of liquid crystal cells disposed around the pixel regions may be changed due to the electric field between the data lines DL and the shield lines SL, thereby occurring the light leakage. In order to prevent light leakage around the pixel regions due to the electric field between the data lines DL and the shield lines SL, black matrices above the data lines DL may be formed to have a width (hereinafter, referred to as a “first width”) sufficient to cover the data lines DL and the shield lines SL. On the other hand, the common lines disposed alternately with the data lines DL do not generate an electric field together with other adjacent components, with the result that black matrices above the common lines CL may be formed to have a small width (hereinafter, referred to as a “second width”) similar to the common lines CL, irrespective of light leakage around the pixel regions.
If the difference between the first width and the second width is equal to or greater than a critical value, however, the black matrices BM(DL) above the data lines are more visible than the black matrices BM(CL) above the common lines, as shown in FIG. 2B. Such a visibility problem disturbs clear distinction between neighboring pixels between which the corresponding common lines CL are disposed, with the result that image quality is reduced.
In order to prevent reduction of image quality due to the visibility problem, therefore, the black matrices above the common lines CL must be formed to have a width similar to the first width. If the width of the black matrices above the common lines CL is increased, however, an aperture ratio (an area ratio of a light discharge region to a display region) is reduced unnecessarily.